1. Field of the Invention
The present invention relates to compositions and methods for depositing a metal layer. More particularly the present invention relates to compositions for depositing a cobalt layer on an integrated circuit device having high purity and good step coverage and to methods of forming a metal layer using the same.
2. Description of the Related Art
In an information society, an integrated circuit device having rapid data transferring speed is required so as to process information rapidly. However, as the integrated circuit device becomes highly integrated, the manufacturing process may become difficult. As the length of a gate electrode becomes shorter, and the junction depth of source and drain electrodes becomes shallow, resistance between the gate electrode and the source/drain electrode increases. As the resistance increases, the operational speed of the integrated circuit device decreases while the power consumption of the integrated circuit device increases. Due to the demand for faster processing speeds in integrated circuits, the size of features in these circuits has been steadily shrinking. However, as device dimensions are scaled down, increasingly stringent requirements are being placed on the properties and performance of the materials used. These stringent conditions have increased impurities in the integrated circuit devices.
In order to avoid the above-mentioned problem, a metal-silicide layer, such as a tungsten-silicide layer, titanium-silicide layer, cobalt-silicide layer, etc., can be formed on a gate electrode region, and source and drain electrode regions. It has been found that the cobalt-silicide layer has a low resistivity, low silicon consumption and high thermal and chemical stability. Thus, the cobalt-silicide layer can be widely used for highly integrated circuit devices.
In the past, in order to form the cobalt-silicide layer, cobalt was deposited on a silicon substrate or silicon pattern to form a cobalt layer via physical vapor deposition (hereinafter, referred to as PVD) method. The cobalt layer then would undergo a thermal process so that cobalt reacts with silicon to form the cobalt-silicide layer. However, when the cobalt layer is deposited via the PVD method step coverage of the cobalt layer is often deteriorated. Regions where the cobalt layer was deposited often had a misuniform or curved pattern, which affected the overall results of the integrated circuit device.
FIG. 1 illustrates a cross-sectional view showing a cobalt layer deposited via a general PVD method known in the art. In FIG. 1, a minute gate pattern 102 is formed on an integrated circuit device 100. A spacer 104 is formed at a side of the gate pattern 102. A cobalt layer 106 covers the gate pattern 102, the spacer 104, and the integrated circuit device 100. FIG. 1 illustrates that the cobalt layer 106 is deposited via a PVD method. The cobalt layer 106 deposited by the PVD method does not have a uniform thickness. FIG. 1 illustrates that the cobalt layer 106 formed on the integrated circuit device 100 and spacer 104 between the gate patterns 102 has a thinner thickness than the cobalt layer 106 formed on other portions of the integrated circuit device. When the thickness of the cobalt layer 106 is not uniform, the subsequent cobalt-silicide layer formed via the thermal process is also not uniform. Thus, the integrated circuit is not reliable. In order to deposit the cobalt layer 106 uniformly a chemical vapor deposition (CVD) method has been developed.
For example, U.S. Pat. No. 6,346,477, issued to Kaloyeros et al., discloses a method of depositing a cobalt layer on a silicon substrate via CVD method using Co(CO)3NO as a precursor. However, in Kaloyeros et al., the silicon is oxidized by oxygen of the precursor or by oxygen generated during CVD as a byproduct, so that an oxidation layer is formed at an interface between the silicon face and the cobalt layer. This oxidation layer prevents a reaction between the cobalt and silicon, thus preventing high purity for the integrated circuit device.
Other CVD processes for the deposition of cobalt and cobalt disilicide are known in the art. Ivanova et. al. disclosed a CVD process for the formation of cobalt films from cobalt tricarbonyl nitrosyl, Co(CO)3NO (J. Electrochem. Soc., 146, 2139–2145 (1999)). West et al. (U.S. Pat. No 4,814,294) described the use of a cobalt source precursor along with silane as a silicon source precursor for the deposition of cobalt disilicide. Dicobalt octacarbonyl, Co2(CO)8 and cobalt tricarbonyl nitrosyl Co(CO)3No are known as suitable cobalt source precursors. Rhee et al. reported a CVD approach for the growth of epitaxial CoSi2 through a two step process which involved, in a first step, the deposition of a Co—C film through the CVD decomposition of the cobalt source dicobalt octacarbonyl, Co2(CO)8, or cyclopentadienyl-cobalt dicarbonyl, C5H5CO(CO)2 (J. Electrochem. Soc., 146, 2720 (1999)). This was followed, in a second step, by an ex-situ thermal annealing step at 800° C. to form the epitaxial CoSi2 phase. Unfortunately, the process described has several drawbacks which have prevented commercial acceptance. First, dicobalt octacarbonyl has some serious limitations as a cobalt source precursor. Thermodynamically favorable polymerization and hydrogenation reactions in a CVD chamber compete with the formation of pure cobalt. These reactions include polymerization reactions in the gas phase and reactions with hydrogen yielding highly volatile and extremely unstable hydrocobalt tetracarbonyl compounds. The compound is also known to be unstable during storage, even under vacuum or inert atmosphere. Second, the process also requires a high temperature annealing step (over 800° C.) to form the desired CoSi2 epitaxial phase. Rhee et al. also discloses a method of forming cobalt layer on a silicon substrate by metal organic chemical vapor deposition (MOCVD) using Co2(CO)8, Co(C5H5)2, Co(C5H5)(CO)2 and CoCF3(CO)4 as precursors (Applied physics letters vol. 74 no. 7 (1999)). However, this method results in an increase in the resistivity of the cobalt layer because of numerous impurities. Accordingly, it may be beneficial to produce new compositions and methods for depositing a cobalt layer on an integrated circuit device.